This invention is related to micro-lens aided silver halide photography.
In conventional photography, it is well known to record images by controllably exposing a photosensitive element to light from a scene. Typically, such a photosensitive element comprises one or more photosensitive layers supported by a flexible substrate such as film and/or a non-flexible substrate such as a glass plate. The photosensitive layers, which can have one or more light sensitive silver halide emulsions along with product appropriate imaging chemistry, react to the energy provided by the light from the scene. The extent of this reaction is a function of the amount of light received per unit area of the element during exposure. The extent of this reaction is greater in areas of the element that are exposed to more light during an exposure than in areas that are exposed to less light. Thus, when light from the scene is focused onto a photosensitive element, differences in the levels of light from the scene are captured as differences in the extent of the reaction in the layers. After a development step, the differences in the extent of the reaction in the layers appear as picture regions having different densities. These densities form an image of the original scene luminance distribution.
It is characteristic of silver halide emulsions to have a non-linear response when exposed to ambient light from a scene. In this regard a photosensitive element has a lower response threshold that defines the minimum exposure at which the incorporated emulsions and associated chemistry begins to react so that different levels of exposure enable the formation of different densities. This lower threshold ultimately relates to the quantum efficiency of individual silver halide emulsion grains. Typically, all portions of a photosensitive element that are exposed to light at a level below the lower response threshold have a common appearance when the photosensitive element is developed.
Further, a photosensitive element also has an upper response threshold that defines the exposure level beyond which the emulsion and associated chemistries no longer enable the formation of different densities. Typically, all portions of an element that are exposed at a level above the upper response threshold will again have a common appearance after the photosensitive element is developed.
Thus photosensitive elements that use silver halide emulsions can be said to have both a lower response threshold and an upper response threshold which bracket a useful range of exposures wherein the photosensitive element is capable of reacting to differences in exposure levels by recording a contrast pattern with contrast differences that are differentiable. The exposure levels associated with these lower and upper thresholds define the exposure latitude of the photosensitive element. To optimize the appearance of an image, therefore, it is typically useful to arrange the exposure so that the range of exposure levels encountered by the photosensitive element during exposure is within the latitude or useful range of the photosensitive element.
Many consumer and professional photographers prefer to use photosensitive elements, camera systems, and photography methods that permit image capture over a wide range of photographic conditions. One approach to meeting this objective is to provide photosensitive elements with extremely wide latitude. However, extremely wide latitude photosensitive elements are fundamentally limited by the nature of the response of the individually incorporated silver halide grains to light. Accordingly, it is common to provide camera systems and photography methods that work to effectively extend the lower response limit and upper response limit of a photosensitive element by modifying the luminance characteristics of the scene. For example, it is known to effectively extend the lower response limit of the photosensitive element by providing supplemental illumination to dark scenes.
It is also known to increase the quantity of the light acting on a photosensitive element without providing supplemental illumination by using a taking lens system designed to pass a substantial amount of the available light from the scene to the photosensitive element during an exposure. However, lenses that pass a substantial amount of light also inherently reduce the depth-of field of the associated camera system. This solution is thus not universally suitable for pictorial imaging with fixed focus cameras since scenes may not then be properly focused. This solution is also not preferred in variable focused cameras as such lens systems can be expensive, and difficult to design, install and maintain.
There is a direct relationship between the duration of exposure and quantity of light from the scene that strikes the photosensitive element during an exposure. Accordingly, another way known in the art for increasing the amount of light acting on a photosensitive element during an exposure is to increase the duration of the exposure using the expedient of a longer open shutter. This, however, degrades upper exposure limits. Further, increased shutter open time can cause the shutter to remain open for a period that is long enough to permit the composition of a scene to evolve. This results in a blurred image. Accordingly, there is a desire to limit shutter open time.
Thus, what is also needed is a less complex and less costly camera system and photography method allowing the capture of images using conventional shutter open times and particularly with cameras having a fixed shutter time.
Another way to increase the quantity of the light acting on a photosensitive element during an exposure is to use a conventional taking lens system to collect light from a scene and to project this light from the scene onto an array of micro-lenses such as an array of linear lenticular lenses that are located proximate to the photosensitive element. An example of this is shown in U.S. Pat. No. 1,838,173 filed by Chretien on Jan. 9, 1928. Each micro-lens concentrates a portion of the light from the scene onto associated areas of a photosensitive element. By concentrating light in this manner, the amount of light incident on each concentrated exposure area of the photosensitive element is increased to a level that is above the lower response threshold of the film. This permits an image to be formed by contrast patterns in the densities of the concentrated exposure areas.
Images formed in this manner are segmented: the concentrated exposure areas form a concentrated image of the scene and remaining portions of the photosensitive element form a pattern of unexposed artifacts intermingled with the concentrated image. In conventionally rendered prints of such images this pattern has an unpleasing low contrast and a half-tone look much like newspaper print.
However, a recognizable image can be obtained from such segmented images by projection under quite specific conditions. These conditions occur precisely when the spatial relationship between the effective camera aperture, the micro-lens array and the light sensitive element established at exposure in the camera is reproduced in the projector. This system can be cumbersome because a functional real image is produced at a position and magnification dictated by the original scene to camera lens arrangement. If a projection lens identical to the camera taking lens is positioned so as to mimic the camera lens to image relationship that existed at image taking, the reconstructed image will appear at the position of the original object with the size of the original object. Other lens and spatial relationship combinations result in incomplete image reconstruction and the formation of the dots and lines reminiscent of newspaper print. Thus, the micro-lens or lenticular assisted low light photography of the prior art is ill suited for the production of prints or for use in high quality markets such as those represented by consumers and professional photographers.
Micro-lens arrays, and in particular, lenticular arrays have found other applications in photography. For example, in the early days of color photography, linear lenticular image capture was used in combination with color filters as means for splitting the color spectrum to allow for color photography using black and white silver halide imaging systems. This technology was commercially employed in early color motion picture capture and projection systems as is described in commonly assigned U.S. Pat. No. 2,191,038. In the 1950s it was proposed to use lenticular screens to help capture color images using black and white photosensitive element in instant photography U.S. Pat. No. 2,922,103. In the 1970s, it was proposed to expose a photosensitive element through a moving lenticular screen U.S. Pat. No. 3,954,334 to achieve gradual tinting. Also in the 1970""s, U.S. Pat. No., 3,973,953 filed by Montgomery describes an arrangement of micro-lenses and a photosensitive material in which the photosensitive material is kept out of focus to achieve increased photosensitive latitude at the cost of forming imperfect images. In the 1980""s, U.S. Pat. No. 4,272,186 filed by Plummer describes a related arrangement of micro-lenses and a photosensitive material further comprising a screen to control the exposure contrast of the system. Here, a separation of at least 2.5 mm is required between the surface of the photosensitive material and the surface of the micro-lens array. This long focal length practically limits the range of useful microlens sizes and f-numbers to those compatible with direct view prints but not compatible with enlargements as are required from modem camera films suitable for employed in hand-held cameras. By minimizing the size of the unexposed areas, the line pattern became almost invisible and was therefore less objectionable.
Finally, in the 1990""s linear lenticular-ridged supports having three-color layers and an antihalation layer were employed for 3-D image presentation materials. These linear lenticular arrays were used to form interleaved print images from multiple views of a scene captured in multiple lens cameras. The interleaved images providing a three dimensional appearance. Examples of this technique are disclosed in U.S. Pat No. 5,464,128 filed by Lo et al. and in U.S. Pat. No. 5,744,291 filed by Ip. It is recognized that these disclosures relate to methods, elements and apparatus adapted to the formation of 3-D images from capture of multiple scene perspectives that are suitable for direct viewing. They fail to enable photography with shutter times suitable for use in hand-held cameras.
U.S. Pat. No. 5,649,250, filed by Sasaki, U.S. Pat. No. 5,477,291 filed by Mikami et al. and Japanese Patent Publication 2001-147,466 filed by Hiroake et al. describe the replacement of single lenses in cameras by multiple instances (eight to sixteen) of smaller lenses to allow either simultaneous capture of multiple instances of the same image on a single frame of film stock or sequential capture of distinct images to enable, for example analysis of such athletic motion as golf swings.
Thus, while micro-lens assisted photography has found a variety of uses, it has yet to fulfill the original promise of effectively extending the lower response threshold of a photosensitive element to permit the production of commercially acceptable prints from images captured at low scene brightness levels. What is needed, therefore, is a method and apparatus for capturing lenticular images on a photosensitive element and using the captured photosensitive element image to form a commercially acceptable print or other output.
It can also occur that it is useful to capture images under imaging conditions that are above the upper response threshold of the photosensitive element. Such conditions can occur with bright scenes that are to be captured under daylight, snow pack and beach situations. Typically, cameras use aperture control, shutter timing control and filtering systems to reduce the intensity of light from the scene so that the light that confronts the photosensitive element has an intensity that is within the upper limit response of the photosensitive element. However, these systems can add significant complexity and cost to the design of the camera. Further, the expedient of using a lens with a more open aperture to improve the lower threshold limit as discussed earlier simultaneously passes more light and degrades the exposure at the upper response threshold. Thus, what is also needed is a simple, less costly, camera system and photography method for capturing images over a range of exposure levels including exposure levels that are greater than the upper response limit of the photosensitive element.
Novel methods and apparatus for employing micro-lenses to improve the sensitivity and scene capture latitude of silver halide films along with methods to form useful images from micro-lens mediated scene capture have been disclosed in commonly assigned U.S. patent application Ser. No. 10/167,794 entitled xe2x80x9cIMAGING USING SILVER HALIDE FILMS WITH MICRO-LENS CAPTURE AND OPTICAL RECONSTRUCTION,xe2x80x9d filed on Jun. 12, 2002, by Irving and Szajewski, and U.S. patent application Ser. No. 10/170,148 entitled xe2x80x9cIMAGING USING SILVER HALIDE FILMS WITH MICRO-LENS CAPTURE, SCANNING AND DIGITAL RECONSTRUCTION,xe2x80x9d filed on Jun. 12, 2002, by Szajewski and Irving. These disclosures describe arrays of micro-lenses formed into a film base, on a film surface or supplied as free-standing micro-lens arrays which accept light from a primary camera lens and converge the accepted light through their optically transmissive material at a focal plane sufficiently coincident with the light sensitive areas of a silver halide film to enable improved imaging.
In the case of micro-lenses formed into an optically transparent material, the focal length is practically set by the thickness of the material, and this set focal length along with the refractive index of the constituent optically transmissive material defines the required radius of curvature of the individual micro-lenses. This defined radius of curvature in turn sets an upper limit on the aperture of the individual micro-lenses and the effective f-number or converging power of the micro-lenses, as well as the number of micro-lenses that can be packed per unit area or the micro-lens pitch. Free standing arrays of micro-lenses having the very fine pitch used in high resolution imaging require short focal lengths and therefore are typically made from very thin lenticular materials. Such thin lenticular materials can be difficult to manufacture reproducibly and can be difficult to mount with sufficient flatness and rigidity at the focal plane of a camera. Further, the short focal distances of micro-lenses having the very fine pitch used in high resolution imaging requires a flatness and rigidity of the photosensitive element that can be difficult to achieve.
In one aspect of the present invention, a camera is provided. The camera has a primary lens adapted to focus light from a scene and an array of micro-lenses with each micro-lens having a light receiving surface to receive light from the primary lens and a light focusing surface confronting a photosensitive element. The light focusing surface is adapted to concentrate the received light onto the photosensitive element. A spacer positions the photosensitive element separate from the light focusing surfaces. A shutter assembly controllably passes light from the scene to the array of micro-lenses.
In another aspect of the present invention, what is provided is a camera for recording images, the camera having a primary lens adapted to focus light from a scene to form an image of the scene at an imaging plane, and a shutter assembly for controllably passing light from the scene to the imaging plane. An array of micro-lenses is provided with each micro-lens having a receiving surface positioned at the imaging plane to receive light from the primary lens and with each micro-lens having a focusing surface adapted to focus received light to form an image between a near focus distance and a far focus distance. A gate positions the photosensitive element between the near and far focus distances, at a distance between 5 and 1500 micro-meters from the focusing surfaces of the micro-lenses.
In still another aspect of the present invention, a camera for recording images on a photosensitive element having an emulsion for recording an image when exposed to light within a predefined range of exposures. The camera has a camera body with an aperture having a taking lens system for focusing light from a scene. A gate is adapted to position the photosensitive element to confront the aperture. An array of micro-lenses is disposed between said aperture and said gate with said array adapted to receive light from the primary lens system and to pass the light through a light focusing surface confronting the photosensitive element wherein the light focusing surface is adapted to fracture light from the scene into a first fraction and a second fraction. The first fraction of light from the scene is concentrated to form a first image on a first portion of the photosensitive element when light from the scene is within a first range. The second fraction of light from the scene passes onto the photosensitive element to form a second image on a second portion of the photosensitive element. When light from the scene is within a second range, a shutter controllably permits light from the scene to expose the photosensitive element for a predefined period of time, said predefined period of time being sufficient to form an image on said second portion of the photosensitive element when light from the scene is within the second range.